The present invention relates to a fuel control device and method for an internal combustion engine, such as a gasoline engine for a motor vehicle, in which the fuel quantity to be injected is controlled by estimating an accurate air flow rate at the engine cylinder port flowing into the respective engine cylinders by making use of a heat generating resistor type air flow meter.
Many kinds of fuel supply quantity control devices and methods for an internal combustion engine, such as a gasoline engine for a motor vehicle, are known. One example is a device of the type which operates to obtain an estimated pressure at the engine intake manifold by digital-filtering the signal obtained from a heat generating resistor type air flow meter, such as a hot wire type air flow meter. This is accomplished by making use of a difference equation to estimate the air flow rate at the engine cylinder port flowing into the respective engine cylinders by accessing a predetermined cylinder flow-in air flow rate map defined by the obtained estimated pressure at the engine intake manifold and the engine rotating number and to control the fuel supply quantity based upon the estimated cylinder flow-in air flow rate. This type of fuel supply quantity control device has the advantages that no intake air temperature compensation is needed because the fuel quantity is determined by making use of the heat generating resistor type air flow meter and that certain adverse effects, such as manifold charge, are eliminated because the pressure in the intake manifold, an internal state variable, is employed for the determination. Such operation is known as a fuel supply quantity control method having a high accuracy and tracking characteristic.
JP-A-55-146241(1980), JP-A-55-148926(1980), JP-A-62-87648(1987), JP-A-64-32050(1989), JP(PCT)-A-1-501077(1989) and JP-A-1-240753(1989) disclose examples of the above explained conventional devices and methods.
The above conventional devices and methods did not take into account the convergence period encountered at the initial period of operation in the course of their digital filtering process; therefore there was a problem that the starting-up of the internal combustion engine (hereinafter simply called an engine) was difficult because, during starting-up of the engine, many kinds of data in the control unit tend to be disturbed and deviate from their proper conditions.